This invention relates to light emitting devices comprising a UV/blue light emitting diode (LED) and a UV/blue excitable, green light emitting phosphor. It finds particular application in combination with a blend of phosphors, which emit in the blue, green, and red wavelengths, for converting LED-generated ultraviolet (UV) radiation into white light for general illumination purposes. It should be appreciated, however, that the invention is also applicable to the conversion of radiation from UV/blue lasers and other UV sources to green light.
The advent of GaN-based epitaxial structures has lead to the development of UV and or blue (UV/blue) light emitting devices, including light emitting diodes (LEDs) and lasers. By combination of the light emitting device with a phosphor, generation of visible light (e.g., red, blue, or white light) is achieved. The phosphor transforms the UV or blue radiation into light of longer wavelength, for example, by employing a blue absorbing, yellow emitting phosphor, such as Y3Al5O12xe2x80x94Ce3+ (commonly referred to as YAG-Ce), obtainable from Nichia Chemical Company.
The YAG-Ce phosphor converts LED blue radiation into yellow light. This produces a white field with a color rendering index (CRI) of about 77 and a color temperature ranging from about 6000 K to 8000 K. For some applications, conversion of UV/blue light from an LED to visible light using phosphors may be more attractive than the direct application of visible LEDs. Such UV/blue LED phosphor devices, for example, offer the opportunity to encompass a wider color range, which is important for display as well as for illumination applications.
Recently, UV LEDs have been developed which efficiently convert the applied electrical energy into an ultraviolet emission at about 371 nm. There remains a need for a phosphor which converts this radiation to visible light in the green portion of the spectrum.
The present invention provides a new and improved phosphor and method of formation, which overcomes the above-referenced problems and others.
In an exemplary embodiment of the present invention a light source is provided. The light source includes a light emitting component which emits light at a first wavelength and a phosphor material positioned to receive the light emitted by the light emitting component The phosphor material includes a green-emitting phosphor which converts a portion of the light of the first wavelength to light of a second, longer wavelength, the green-emitting phosphor having the general formula LnBO3: Ce3+, Tb3+ where:
Ln includes one ore more of Sc, Y, La, Gd, Lu, and other lanthanide elements. The phosphor preferably has the formula LnxBO3: Ce3+y, Tb3+z where:
x=1xe2x88x92(y+z);
0xe2x89xa6xxe2x89xa60.98;
0.01xe2x89xa6yxe2x89xa60.5; and
0.01xe2x89xa6zxe2x89xa60.5.
In another exemplary embodiment of the present invention a method of converting UV/blue light to light in the green region of the electromagnetic spectrum is provided. The method includes converting the UV/blue light with a phosphor of the general formula LnxBO3: Ce3+y, Tb3+z, as described above.
In another exemplary embodiment of the present invention a phosphor material having the general formula LnxBO3: Ce3+y, Tb3+z is provided.
One advantage of the present invention is the provision of a green-emitting phosphor having good color rendering which converts UV radiation to green light with a high efficiency.
Another advantage of the present invention is a phosphor blend comprising a green-emitting phosphor for converting radiation from a UV/blue light emitting diode to visible light.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments